The invention is directed to an improved fuel injection valve for internal combustion engines.
One fuel injection valve of this type with which this invention is concerned is known from German Patent Disclosure DE 196 18 650 A1, for instance. Such a fuel injection valve has a valve body, in which a bore with a longitudinal axis is embodied, and a valve seat is embodied on the end of the bore toward the combustion chamber. In the region of the valve seat there is at least one injection opening in the valve body that connects the bore with the combustion chamber of the engine. In the bore, a valve member is disposed longitudinally displaceably, being guided in a portion of the bore remote from the combustion chamber. On the end toward the combustion chamber, the valve member changes into a sealing face, which cooperates with the valve seat and thus controls the at least one injection opening. Between the valve member and the wall of the bore, a pressure chamber is formed that can be filled with fuel at high pressure. Because of the fuel pressure in the pressure chamber, the valve member moves counter to a closing force, so that depending on the ratio between the closing force and the hydraulic force on the valve member, the injection opening is opened or closed. The known fuel injection valve has the disadvantage, however, that because of the fuel, which is introduced into the valve body at very high pressure, deformation of the pressure chamber and hence bulging out of the valve body occurs. This has effects especially on the points where the valve member touches the valve body, that is, on the one hand the guided portion of the valve member and on the other the valve seat. As a result of the deformation of the valve body in the region of the pressure chamber, which essentially takes the form of a radial widening of the valve body, the play between the valve member and the valve body can be altered in the region of the guidance. This can lead to increased wear and hence a shorter service life of the fuel injection valve. Moreover, the valve seat, which is embodied essentially conically, tilts outward somewhat because of the widening. This tilting is unwanted, since it affects the opening pressure, that is, the pressure in the pressure chamber at which the valve member moves counter to the closing force, and increases wear in the region of the valve seat.
The fuel injection valve of the invention has the advantage over the prior art that the strength of the valve body is increased, so that the deformation of the valve body caused the pressure in the pressure chamber is reduced. To that end, the valve body is surrounded, in the region of the pressure chamber, by a sleeve that has anisotropic strength properties. As a result, the tangential stiffness of the valve body can be increased, and thus the disadvantages resulting from deformation of the valve body because of the high fuel pressure in the pressure chamber are avoided.
In an advantageous embodiment of the sleeve, this sleeve has a greater tensile strength in the tangential direction, relative to the longitudinal axis of the bore, than in the longitudinal direction. Since the deformation of the valve body under pressure occurs primarily in the radial direction, reinforcing the valve body in the tangential direction suffices to achieve the desired stiffness.
In an advantageous feature, the sleeve has a greater modulus of elasticity in the tangential direction than the steel from which the valve body is made. As a result, part of the valve body can be replaced by the sleeve, so that the total outer dimensions of the valve body are increased only insignificantly, if at all, as a result of the sleeve.
In an advantageous feature, the sleeve contains fibers, at least some of which extend at least approximately in the tangential direction. Such composite materials that contain fibers can be manufactured with their strength properties directionally dependent in a targeted way, so that their strength properties can be adjusted over wide ranges.
In a further advantageous feature, the fiber are embodied as carbon fibers. Such carbon fibers are extremely tear-resistant in their longitudinal direction and have a high modulus of elasticity, so that moduli of elasticity and tensile strengths are achievable that are markedly higher than those of steel.
In another advantageous feature, the carbon fibers are embodied in a matrix of epoxy resin. Such carbon-fiber and epoxy-resin composite materials are well known from the prior art and can thus be put into any arbitrary shape using known techniques.
Epoxy resin here is a thermosetting plastic, so that no flowing of the material occurs under the influence of temperature.
In another advantageous feature, the carbon fibers are embodied in a matrix of graphite. A carbon-fiber and graphite composite has the advantage of remaining stable up to high temperatures of 200xc2x0 C. to 300xc2x0 C. and of thus being suited without limitation for use in a fuel injection valve.
In another advantageous feature, the carbon fibers are embedded in a matrix of metal, which is preferably aluminum. Such composites of carbon fibers and metal have even better temperature resistance and are suitable for even the greatest thermal loads in internal combustion engines.